1. Slide 0 Copyright © 2004. Mosby Inc. All Rights Reserved. The Muscular System

2. Slide 1 Copyright © 2004. Mosby Inc. All Rights Reserved. Introduction Muscular tissue enables the body and its parts to move  Movement caused by ability of muscle cells (called fibers) to shorten or contract  Muscle cells shorten by converting chemical energy (obtained from food) into mechanical energy, which causes movement  Three types of muscle tissue exist in the body

3. Slide 2 Copyright © 2004. Mosby Inc. All Rights Reserved. Muscle Tissue Types of muscle tissue  Skeletal muscle—also called striated or voluntary muscle  Is 40% to 50% of body weight (“red meat” attached to bones)  Microscope reveals crosswise stripes or striations  Contractions can be voluntarily controlled (Cont’d…)

4. Slide 3 Copyright © 2004. Mosby Inc. All Rights Reserved. (…Cont’d)  Cardiac muscle—composes bulk of heart  Cardiac muscle cells branch frequently  Characterized by unique dark bands called intercalated disks  Interconnected nature of cardiac muscle cells allows heart to contract efficiently as a unit (Cont’d…) Muscle Tissue

5. Slide 4 Copyright © 2004. Mosby Inc. All Rights Reserved. Muscle Tissue  Nonstriated muscle or involuntary muscle— also called smooth or visceral muscle  Lacks cross stripes or striation when seen under a microscope; appears smooth  Found in walls of hollow visceral structures such as digestive tract, blood vessels, and ureters  Contractions not under voluntary control; movement caused by contractions is involuntary  Function—all muscle cells specialize in contraction (shortening)

6. Slide 5 Copyright © 2004. Mosby Inc. All Rights Reserved. Structure of Skeletal Muscle Structure  Each skeletal muscle is an organ composed mainly of skeletal muscle cells and connective tissue  Most skeletal muscles extend from one bone across a joint to another bone (Cont’d…)

7. Slide 6 Copyright © 2004. Mosby Inc. All Rights Reserved. Structure of Skeletal Muscle (…Cont’d)  Parts of a skeletal muscle  Origin—attachment to the bone that remains relatively stationary or fixed when movement at the joint occurs  Insertion—point of attachment to the bone that moves when a muscle contracts  Body—main part of the muscle (Cont’d…)

8. Slide 7 Copyright © 2004. Mosby Inc. All Rights Reserved. Structure of Skeletal Muscle (…Cont’d)  Muscles attach to the bone by tendons— strong cords of fibrous connective tissue; some tendons enclosed in synovial-lined tubes and are lubricated by synovial fluid; tubes called tendon sheaths  Bursae—small synovial-lined sacs containing a small amount of synovial fluid; located between some tendons and underlying bones (Cont’d…)

9. Slide 8 Copyright © 2004. Mosby Inc. All Rights Reserved. Structure of Skeletal Muscle (…Cont’d) Microscopic structure  Contractile cells called fibers—grouped into bundles  Fibers contain thick myofilaments (containing the protein myosin) and thin myofilaments (composed of actin) (Cont’d…)

10. Slide 9 Copyright © 2004. Mosby Inc. All Rights Reserved. Structure of Skeletal Muscle (…Cont’d)  Basic functional (contractile) unit called sarcomere; sarcomeres separated from each other by dark bands called Z lines  Sliding filament model explains mechanism of contraction o Thick and thin myofilaments slide past each other as a muscle contracts o Contraction requires calcium and energy-rich ATP molecules

11. Slide 10 Copyright © 2004. Mosby Inc. All Rights Reserved. Functions of Skeletal Muscle Movement  Muscles produce movement; as a muscle contracts, it pulls the insertion bone closer to the origin bone; movement occurs at the joint between the origin and the insertion (Cont’d…)

12. Slide 11 Copyright © 2004. Mosby Inc. All Rights Reserved. Functions of Skeletal Muscle (…Cont’d)  Groups of muscles usually contract to produce a single movement o Prime mover—muscle whose contraction is mainly responsible for producing a given movement o Synergist—muscle whose contractions help the prime mover produce a given movement o Antagonist—muscle whose actions oppose the action of a prime mover in any given movement (Cont’d…)

13. Slide 12 Copyright © 2004. Mosby Inc. All Rights Reserved. Functions of Skeletal Muscle (…Cont’d) Posture  A specialized type of muscle contraction, called tonic contraction, enables us to maintain body position  In a tonic contraction, only a few of a muscle’s fibers shorten at one time  Tonic contractions produce no movement of body parts (Cont’d…)

14. Slide 13 Copyright © 2004. Mosby Inc. All Rights Reserved. Functions of Skeletal Muscle (…Cont’d)  Tonic contractions maintain muscle tone called posture  Good posture reduces strain on muscles, tendons, ligaments, and bones  Poor posture causes fatigue and may lead to deformity (Cont’d…)

15. Slide 14 Copyright © 2004. Mosby Inc. All Rights Reserved. Functions of Skeletal Muscle (…Cont’d) Heat production  Survival depends on the body’s ability to maintain a constant body temperature  Fever—an elevated body temperature; often a sign of illness  Hypothermia—a reduced body temperature  Contraction of muscle fibers produces most of the heat required to maintain normal body temperature

16. Slide 15 Copyright © 2004. Mosby Inc. All Rights Reserved. Fatigue Reduced strength of muscle contraction Caused by repeated muscle stimulation Repeated muscular contraction depletes cellular ATP store and outstrips the ability of the blood supply to replenish oxygen and nutrients (Cont’d…)

17. Slide 16 Copyright © 2004. Mosby Inc. All Rights Reserved. Fatigue (…Cont’d) Contraction in the absence of adequate oxygen produces lactic acid, which contributes to muscle soreness Oxygen debt—term used to describe the metabolic effort to burn excess lactic acid that may accumulate during prolonged periods of exercise; the body is attempting to return the cells’ energy and oxygen reserves to pre- exercise levels

18. Slide 17 Copyright © 2004. Mosby Inc. All Rights Reserved. Role of Other Body Systems in Movement Muscle functioning depends on the functioning of many other parts of the body Respiratory, circulatory, nervous, muscular, and skeletal systems play essential roles in producing normal movements Multiple sclerosis, brain hemorrhage, and spinal cord injury are examples of how pathologic conditions in other body organ systems can dramatically affect movement

19. Slide 18 Copyright © 2004. Mosby Inc. All Rights Reserved. Motor Unit Stimulation of a muscle by a nerve impulse is required before a muscle can shorten and produce movement A motor neuron is the specialized nerve that transmits an impulse to a muscle, causing contraction (Cont’d…)

20. Slide 19 Copyright © 2004. Mosby Inc. All Rights Reserved. Motor Unit (…Cont’d) A neurotransmitter junction is the specialized point of contact between a nerve ending and the muscle fiber it innervates A motor unit is the combination of a motor neuron with the muscle cell or cells it innervates

21. Slide 20 Copyright © 2004. Mosby Inc. All Rights Reserved. Muscle Stimulus A muscle will contract only if an applied stimulus reaches a certain level of intensity  A threshold stimulus is the minimal level of stimulation required to cause a muscle fiber to contract Once stimulated by a threshold stimulus, a muscle fiber will contract completely, a response called all or none (Cont’d…)

22. Slide 21 Copyright © 2004. Mosby Inc. All Rights Reserved. Muscle Stimulus (…Cont’d) Different muscle fibers in a muscle are controlled by different motor units having different threshold-stimulus levels  Although individual muscle fibers always respond all or none to a threshold stimulus, the muscle as a whole does not  Different motor units responding to different threshold stimuli permit a muscle as a whole to execute contractions of graded force

23. Slide 22 Copyright © 2004. Mosby Inc. All Rights Reserved. Types of Skeletal Muscle Contraction Twitch and tetanic contractions  Twitch contractions are laboratory phenomena and do not play a significant role in normal muscular activity; they are a single contraction of muscle fibers caused by a single threshold stimulus  Tetanic contractions are sustained and steady muscular contractions caused by a series of stimuli bombarding a muscle in rapid succession (Cont’d…)

24. Slide 23 Copyright © 2004. Mosby Inc. All Rights Reserved. Types of Skeletal Muscle Contraction (…Cont’d) Isotonic contractions  Contraction of a muscle that produces movement at a joint  During isotonic contractions, the muscle changes length, causing the insertion end of the muscle to move relative to the point of origin  Most types of body movements such as walking and running are caused by isotonic contractions (Cont’d…)

25. Slide 24 Copyright © 2004. Mosby Inc. All Rights Reserved. Types of Skeletal Muscle Contraction (…Cont’d) Isometric contractions  Isometric contractions are muscle contractions that do not produce movement; the muscle as a whole does not shorten  Although no movement occurs during isometric contractions, tension within the muscle increases

26. Slide 25 Copyright © 2004. Mosby Inc. All Rights Reserved. Effects of Exercise on Skeletal Muscles Exercise, if regular and properly practiced, improves muscle tone and posture, results in more efficient heart and lung functioning, and reduces fatigue (Cont’d…)

27. Slide 26 Copyright © 2004. Mosby Inc. All Rights Reserved. Effects of Exercise on Skeletal Muscles (…Cont’d) Effects of Exercise on Skeletal Muscles  Muscles undergo changes related to the amount of work they normally do  Prolonged inactivity causes disuse atrophy  Regular exercise increases muscle size, called hypertrophy (Cont’d…)

28. Slide 27 Copyright © 2004. Mosby Inc. All Rights Reserved. Effects of Exercise on Skeletal Muscles (…Cont’d)  Strength training is exercise involving contractions of muscles against heavy resistance  Strength training increases the numbers of myofilaments in each muscle fiber, and as a result, the total mass of the muscle increases  Strength training does not increase the number of muscle fibers (Cont’d…)

29. Slide 28 Copyright © 2004. Mosby Inc. All Rights Reserved. Effects of Exercise on Skeletal Muscles (…Cont’d)  Endurance training is exercise that increases a muscle’s ability to sustain moderate exercise over long periods; it is sometimes called aerobic training  Endurance training allows more efficient delivery of oxygen and nutrients to a muscle via increased blood flow  Endurance training does not usually result in muscle hypertrophy

30. Slide 29 Copyright © 2004. Mosby Inc. All Rights Reserved. Skeletal Muscle Groups Muscles of the head and neck  Facial muscles  Orbicularis oculi  Orbicularis oris  Zygomaticus (Cont’d…)

31. Slide 30 Copyright © 2004. Mosby Inc. All Rights Reserved. MAJOR MUSCLES HEAD AND NECK

32. Slide 31 Copyright © 2004. Mosby Inc. All Rights Reserved. Skeletal Muscle Groups (…Cont’d)  Muscles of mastication  Masseter  Temporal  Sternocleidomastoid—flexes head  Trapezius—elevates shoulders and extends head (Cont’d…)

33. Slide 32 Copyright © 2004. Mosby Inc. All Rights Reserved. MAJOR MUSCLES BACK

34. Slide 33 Copyright © 2004. Mosby Inc. All Rights Reserved. MAJOR MUSCLES UPPER EXTREMITIES

35. Slide 34 Copyright © 2004. Mosby Inc. All Rights Reserved. Skeletal Muscle Groups (…Cont’d) Muscles that move the upper extremities  Pectoralis major—flexes upper arm  Latissimus dorsi—extends upper arm  Deltoid—abducts upper arm  Biceps brachii—flexes forearm  Triceps brachii—extends forearm (Cont’d…)

36. Slide 35 Copyright © 2004. Mosby Inc. All Rights Reserved. MAJOR MUSCLES ABDOMEN

37. Slide 36 Copyright © 2004. Mosby Inc. All Rights Reserved. Skeletal Muscle Groups (…Cont’d) Muscles of the trunk  Abdominal muscles  Rectus abdominis  External oblique  Internal oblique  Transversus abdominis  Respiratory muscles  Intercostal muscles  Diaphragm (Cont’d…)

38. Slide 37 Copyright © 2004. Mosby Inc. All Rights Reserved. MAJOR MUSCLES LOWER EXTREMITIES

39. Slide 38 Copyright © 2004. Mosby Inc. All Rights Reserved. MAJOR MUSCLES PELVIS/ LOWER EXTREMITIES

40. Slide 39 Copyright © 2004. Mosby Inc. All Rights Reserved. Skeletal Muscle Groups (…Cont’d) Muscles that move the lower extremities  Iliopsoas—flexes thigh  Gluteus maximus—extends thigh  Adductor muscles—adduct thighs  Hamstring muscles—flex lower leg  Semimembranosus  Semitendinosus  Biceps femoris (Cont’d…)

41. Slide 40 Copyright © 2004. Mosby Inc. All Rights Reserved. Skeletal Muscle Groups (…Cont’d) Muscles that move the lower extremities  Quadriceps femoris group—extend lower leg  Rectus femoris  Vastus muscles  Tibialis anterior—dorsiflexes foot  Gastrocnemius—plantar flexes foot  Peroneus group—flex foot

42. Slide 41 Copyright © 2004. Mosby Inc. All Rights Reserved. Types of Movements Produced by Skeletal Muscle Contractions Flexion—movement that decreases the angle between two bones at their joint: bending Extension—movement that increases the angle between two bones at their joint: straightening (Cont’d…)

43. Slide 42 Copyright © 2004. Mosby Inc. All Rights Reserved. Types of Movements Produced by Skeletal Muscle Contractions (…Cont’d) Abduction—movement of a part away from the midline of the body Adduction—movement of a part toward the midline of the body Rotation—movement around a longitudinal axis (Cont’d…)

44. Slide 43 Copyright © 2004. Mosby Inc. All Rights Reserved. Types of Movements Produced by Skeletal Muscle Contractions (…Cont’d) Supination and pronation—hand positions that result from rotation of the forearm; supination results in a hand position with the palm turned to the anterior position; pronation occurs when the palm faces posteriorly (Cont’d…)

45. Slide 44 Copyright © 2004. Mosby Inc. All Rights Reserved. Types of Movements Produced by Skeletal Muscle Contractions (…Cont’d) Dorsiflexion and plantar flexion—foot movements; dorsiflexion results in elevation of the dorsum or top of the foot; during plantar flexion, the bottom of the foot is directed downward

46. Slide 45 Copyright © 2004. Mosby Inc. All Rights Reserved. The End